Background of the Invention
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The present invention is suitable for a catheter used
for performing a non-craniotomy minimally invasive treatment
by means of inserting the catheter into a narrow blood vessel
without incising a head in mainly a treatment and a diagnosis
of brain infarction, a cerebral aneurysm or the like. The present
invention relates to a device for detecting a position and an
orientation of an insertion portion of a medical insertion tool,
which is inserted inside a body cavity, from the outside, and
a detecting method therefor. The medical insertion tool is
selected from indwelling tools inside the body cavity such as
a guide wire, an endoscope or a drainage tube for forming a
discharge passage for body fluid, a biliary stent, a high calorie
transfusion tube as well as the catheter.
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When a narrow tubular medical insertion tool such as the
catheter to be inserted into a vein is inserted into a
predetermined position inside a body cavity, it is extremely
important to exactly detect and grasp the current position and
orientation of the medical insertion tool so as to prevent the
insertion portion from straying off, adversely affecting a tissue
of a living body as a result of a state wherein the insertion
portion catches the tissue owing to a friction between the
insertion portion and a surface of the tissue of the living body.
Here, the orientation means a direction and a twist of a tip
of the insertion portion.
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As a means for detecting the position and orientation
of the medical insertion tool having the above important role,
conventionally, an fluoroscopy has been performed, and also a
means performed through injection of a contrast medium has been
used. However, this requires not only a skillful technique but
also contrivance for decreasing anX-rays exposure amount through
means that the number of times for fluoroscopy is limited so
as to avoid an ill effect on a human body such as a patient or
a person to be operated owing to X-rays exposure, or an operator
wears a protector accompanying unpleasantness and difficulty
in an operation. Moreover, this only provides a two-dimensional
image. So, it has a disadvantage wherein the insertion tool
is not easily inserted and operated. Especially, the blood
vessel inside a skull is narrow, complicatedly wound and has
many branches. So, when it is compared with a cardiac catheter
of which technique has been substantially established, a
treatment and a medical examination through it are difficult
and a time-consuming work. Moreover, it should be avoided to
expose the head to X-rays. Taking the above circumstances into
consideration, it is desired to provide a new method for detecting
a position and an orientation thereof instead of fluoroscopy
so as to decrease the number of times for fluoroscopy.
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As the means for meeting the demand, a research has been
developed for detecting a position and an orientation of a target
(i.e., an insertion portion of a medical insertion tool to be
inserted into a body cavity) by means of the magnetic field.
In case of using the magnetic field so as to detect the position
and the orientation of the target, a relative permeability of
the human body is almost 1, and a distribution of the magnetic
field inside the body cavity can be treated in the same way as
one in the air. If the magnetic field is set to be an appropriate
scale and an appropriate frequency, it has no bad influence on
the human body. It has the above usefulness wherein secondary
problems do not occur in using the medical insertion tool which
is inserted into the body cavity. Noticing the usefulness
obtained as a result of use of the magnetic field, a magnetic
sensor system for detecting a position and an orientation of
the tip of the catheter is proposed as an example of the device
whichmakes it possible to detect the three-dimensional position
and orientation of the insertion portion of the medical insertion
tool. The magnetic sensor system has the following structure:
1) a tip of a catheter to be used as an example of a medical
insertion tool is provided with a magnetic sensor (i.e., a
magnetic filed detecting means) such as a triaxial magnet field
sensor (i.e., triaxial MI sensor) by exerting amorphous wire
magneto-impedance effect elements: 2) an alternating current
magnetic field generated from a biaxial exciting coil (i.e.,
a magnetic field generating means) disposed outside the body
cavity is measured by means of the magnetic sensor disposed on
the tip of the catheter: 3) After a sensor signal is
circuit-processed, it is input to a computer through an A/D
converter, whereby the three-dimensional position and the
orientation of the catheter is sought on the basis of a
predetermined algorism by means of the computer in real time:
4) on the basis of information relating to the position and the
orientation thereof, the catheter is superimposed on a
three-dimensional image of a blood vessel which was input to
the computer by means of CT or MRI, prior to an operation. (cf.
Publication E of Conference of the Institute of Electrical
Engineers of Japan, 2000 Vol. 120, No. 5 PP.211-218).
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However, in the device for detecting a position and an
orientation of a medical insertion tool inside a body cavity
according to the prior art such as the above-mentioned magnetic
sensor system for detecting the position and the orientation
of the catheter tip, it is necessary to dispose plural conductors
such as a coaxial cable along the insertion portion so as to
supply driving electric power for a magnetic sensor to be inserted
in the body cavity, which is attachedly disposed on the tip of
the insertion portion of the medical insertion tool as the
magnetic field detecting means, and fetch a detecting magnetic
field signal detected by the magnetic sensor from the inside
of the body cavity to the outside thereof. This not only results
in an increase of a diameter of the insertion portion, but also
easily leads to an increase of a weight thereof. So, this makes
it further difficult to insert the insertion portion inside the
body cavity such as a blood vessel in a skull, as compared with
the prior art. It further aggravates a problem of adversely
affecting a tissue of a living body as a result of a state wherein
the insertion portion catches the tissue owing to a friction
between the insertion portion and a surface of the tissue of
the living body.
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Inaddition, ithasanotherproblemwhereinanoiseoccurs
or is mixed when electric power is supplied to the inside of
the body cavity and the detectingmagnetic field signal is fetched
from the body cavity. Consequently, S/N ration is reduced,
thereby making it impossible to obtain a high detecting accuracy.
Summary of the Invention
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The present invention has been conducted in view of the
above-discussed circumstances and problems. An object of the
present invention is to provide a small-size and light weight
insertion portion so as to make it possible to be smoothly and
easily inserted into even a narrow body cavity such as a blood
vessel inside a skull, without having a bad influence on a vital
tissue. Moreover, another object thereof is to provide the
device for detecting the position and the orientation of the
medical insertion tool inside the body cavity which makes it
possible to detect the three-dimensional position and
orientation of the insertion tool very accurately while
minimizing a noise and detecting method therefor.
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In order to achieve the above obj ects, a device embodying
the present invention for detecting a position and an orientation
of an insertion portion of a medical insertion tool inside a
body cavity by means of a magnetic field generating means and
a magnetic field detecting means is characterized in that the
magnetic field generating means is attached to the insertion
portion of the medical insertion tool; the magnetic field
generating means is made of a permanent magnet or a ferromagnetic
body which can generate a magnetic field without applying an
electric current to a conductor; and the magnetic field detecting
means is disposed outside the body cavity, and the magnetic field
detecting means including plural magnetic sensors having
triaxial directivity to the magnetic field to be detected, each
of the magnetic sensors having triaxial directivity being formed
by combining plural sensors respectively having uniaxial
directivity.
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A method embodying the present invention of detecting
a position and an orientation of an insertion portion of a medical
insertion tool inside a body cavity by means of a magnetic field
generating means and a magnetic field detecting means comprises
the steps of generating a magnetic field through the magnetic
field generating means made of a permanent magnet or a
ferromagnetic body attached to the insertion portion, without
applying an electric current to a conductor, in a state wherein
the insertion portion thereof is inserted inside the body cavity,
measuring the generated magnetic field by means of the plural
magnetic sensors having the triaxial directivity to the magnetic
field to be detected, which are disposed outside the body cavity,
each of the magnetic sensors having triaxial directivity being
formed by combining plural sensors respectively having uniaxial
directivity and detecting a three dimensional position and a
three dimensional orientation of the insertion portion of the
medical insertion tool.
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The present invention having the above elements is a
device for detecting a three-dimensional position and
orientation of the insertion portion by means of measuring the
magnetic field through the magnetic sensor disposed outside the
body cavity. The magnetic field is distributed in the air in
the almost same way as that of the inside of the body cavity,
and is generated by the permanent magnet or the ferromagnetic
body attached to the insertion portion of the medical insertion
tool to be inserted into the body cavity. So, the present
invention does not require disposing a conductor for supplying
a sensor driving power and a conductor for taking out a detecting
magnetic field signal such as a coaxial cable, along the insertion
portion of the medical insertion tool, which is different from
the prior art. This can achieve a downsized and lightweight
insertion portion of the medical insertion tool. As a result,
it can be smoothly and easily performed to insert the insertion
portion into even the narrow body cavity such as the blood vessel
inside the skull, without having a bad influence on a vital tissue.
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Moreover, it is not necessary to apply an electric current
to the insertion portion of the medical insertion tool to be
inserted in the body cavity. This can make S/N ratio great while
minimizing a magnetic field noise which is a cause of a measurement
error of the magnetic sensor. In addition, in case that a
distance between the permanent magnet or the ferromagnetic body
and the magnetic sensor is long, or in case that the permanent
magnet or the ferromagnetic body has a specific orientation,
the magnetic field to be detected is reduced, and the magnetic
noise becomes relatively greater, thereby increasing the
measurement error. However, in the present invention, plural
magnetic sensors are disposed, the magnetic sensors have triaxial
directivity to the magnetic field to be detected. From among
the plural magnetic sensors, we select only the sensors located
in places where a distance between the permanent magnet or the
ferromagnetic body and the magnetic sensor is short, and where
the influence of the orientation is less and the magnetic field
to be detected is great. Then, the magnetic signals measured
by the abovementioned sensor are selectively used.
Consequently, the influence of the distance and the orientation
can be minimized to decrease the measurement error, thereby
making it possible to detect the three-dimensional position and
orientation of the insertion portion of the predetermined medical
insertion tool accurately.
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Especially, three or more magnetic sensors, which work
as the magnetic field detecting means in the present invention,
are equally spaced around a scope to be detected, thereby making
it possible to select and use only the magnetic field signals
measured by at least two magnetic sensors located in places where
there is a less reduction of the magnetic field to be detected
under the influence of the distance and the orientation, in spite
of a detection environment or a condition for disposing magnetic
sensors. By means of using the tiny permanent magnetic or the
ferromagnetic body wherein the generated magnetic field strength
is small, this makes it much easier to insert them into the body
cavity, and it can minimize the measurement errors caused by
the sensors thereby further improving a detecting accuracy of
the position and the orientation of the insertion portion.
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Moreover, though a Hall element or a magnetic inductance
effect element or the like may be used as the magnetic sensors
which is the magnetic field detecting means in the present
invention, it is preferable to use a magneto-impedance effect
element. The magneto-impedance effect element is easily
downsized. Furthermore, through a skin effect of a high magnetic
permeability magnetic body such as an amorphous wire, the
magneto-impedance effect wherein the impedance of the magnetic
body is sensitively changed by the outside magnetic field is
used, thereby obtaining a sensitive measuring accuracy.
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The medical insertion tool of the present invention may
be any one selected from among indwelling tools inside the body
cavity, including a guide wire, an endoscope or a drainage tube,
a biliary stent, a high calorie transfusion tube as well as a
catheter. Especially, in mainly a treatment and a diagnosis
of brain infarction, a cerebral aneurysm or the like, the
insertion tool is used to be inserted in a narrow and complicatedly
wound blood vessel inside the skull. So, it is applicable for
detecting the position and orientation of the catheter, which
needs to be downsized.
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As mentioned above, the present invention provides the
medical insertion tool wherein the permanent magnet or the
ferromagnetic body functioning as the magnetic field generating
means is attached to the insertion portion of the medical
insertion tool in order to detect the position and the orientation
of the medical insertion tool inserted inside the body cavity.
So, as compared with the prior art wherein a magnetic sensor
functioning as the magnetic filed detecting means is attached
to the insertion portion, it is not necessary to dispose electric
conductors for supplying a sensor driving power and for fetching
the detecting magnetic field signal, such as a coaxial cable
along the insertion portion. This can achieve downsizing and
lightening the insertion portion of the medical insertion tool.
As a result, the present invention makes it possible to insert
the insertion portion smoothly and easily into even a narrow
body cavity such as a blood vessel inside a skull, without having
a bad influence on a vital tissue. Moreover, it is not necessary
to apply an electric current to the insertion portion of the
medical insertion tool to be inserted in the body cavity. This
can make S/N ratio great while minimizing a magnetic field noise
which is a cause of measurement error of the magnetic sensor.
Plural magnetic sensors are disposed, the magnetic sensors have
triaxial directivity to the magnetic field t be detected. From
among the plural magnetic sensors, we select the sensor located
in a place where a distance between the permanent magnet or the
ferromagnetic body and the magnetic sensor is short, and where
an influence of the orientation is less and the magnetic field
to be detected is great. Then, the magnetic signals measured
by the abovementioned sensor are selectively used.
Consequently, influence of the distance and the orientation can
be minimized to decrease the measurement error, thereby making
it possible to detect the three-dimensional position and
orientation of the insert on portion of the predetermined medical
insertion tool accurately.
Brief Description of the Drawings
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Fig. 1 is a schematic structural view of a whole of a
system for detecting the position and the orientation of the
tip of the catheter, which illustrates an embodiment wherein
the catheter is used as a medical insertion tool to be inserted
into the body cavity according to the present invention.
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Fig. 2 is an enlarged schematic structural view of the
catheter.
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Fig. 3 is a block structural view of the magnetic field
measurement signal processing circuit connected to a triaxial
MI sensor accompanying the catheter.
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Fig. 4 is a conceptual view illustrating a state wherein
the position and the orientation of the tip of the insertion
portion is detected when non-craniotomy minimally invasive
treatment is performed through the catheter.
Detailed Description of the Preferred Embodiment
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Hereinafter, an embodiment of the invention will be
described with reference to drawings:
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Fig. 1 is a schematic structural view of a device for
detecting a position and an orientation of a medical insertion
tool inside a body cavity, according to the present invention.
The embodiment is applied to a catheter 1 as the medical insertion
tool to be inserted into the body cavity. As shown in Fig. 2,
the catheter 1 includes a narrow tubular insertion portion 2
whose diameter is 100 µ m ~ 1mm, that is, can be inserted into
a blood vessel (i. e., the body cavity) , and an operation portion
3 attached to an base end portion of the insertion portion 2.
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A permanent magnet 4, which functions as a magnetic field
generating means, is fixedly attached to a tip of the insertion
portion 2 in such a catheter 1. The permanent magnet 4 can
generate a magnetic field without applying an electric current
to a conductor. As the permanent magnet 4, columnar NeFeB magnet
or the like whose diameter and length are respectively 2mm and
5mm, and whose surface magnetic flux density is substantially
330mT, are used. The permanent magnet 4 is fixed to the insertion
portion 2 in a settled orientation. A semi-rigid ferromagnetic
body instead of the permanent magnet 4 may be used.
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On the other hand, a magnetic sensor 5, which functions
as a magnetic field detecting means for detecting the magnetic
field to be generated from the permanent magnet 4 inserted into
the blood vessel, is arranged separately from the catheter 1.
The magnetic sensor 5 is an MI sensor having triaxial directivity
(hereinafter called "triaxial MI sensor") by means of amorphous
extreme thin line and magneto-impedance effect element. The
triaxial MI sensor means a triaxial directivity-magnetic sensor
which is formed by combining plural magnetic sensors respectively
having uniaxial directivity. Plural triaxial magnetic sensors
5 are disposed outside the body cavity.
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These triaxial MI sensors 5 are connected to an exclusive
magnetic field measurement signal processing circuit 6. As
shown in Fig. 3 illustrating one sensor having uniaxial
directivity, the magnetic field measurement signal processing
circuit 6 has a structure wherein a high-frequency exciting
current is applied to the MI sensor 5 through an oscillator 7
and a rectification circuit 8, and the outside magnetic field
generated from the permanent magnet 4 is applied thereto , whereby
a modulated wave wherein the high-frequency exciting current
was amplitude-modulated is ratified in an operation- detecting
wave circuit 9, thereby demodulating the wave so as to detect
the modulated wave, i.e., the outside magnetic field, and a
negative feedback signal synchronizing with the outside magnetic
field is generated through an amplifier 10, thereby feeding back
the negative feed back signal to a current which is sent to a
bias magnetic field generating coil 12 through a coil 11, and
biasing it, so as to obtain a sensor output which has an excellent
linear property and wherein a phase was discriminated.
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Next, we will show a method of actually detecting a
position and an orientation of the tip of the insertion portion
2 when a cerebral aneurysm or the like is treated or diagnosed
from an inside of the blood vessel by means of the catheter 1
having the above structure, that is non-craniotomy minimally
invasive treatment is performed. In this case, as shown in Fig.
4, five triaxial MI sensors 5 (a to e) are disposed around a
scope L to be detected in a head portion of a human body, that
is, four triaxial MI sensors 5 are equally spaced around the
scope L and one triaxial MI sensor 5 is disposed over the head
portion. In this state, when the insertion portion 2 of the
catheter 1 is inserted into the blood vessel of the head portion,
the magnetic field generated from the permanent magnet 4 attached
to the tip of the insertion portion 2 is distributed in the air
at an outer periphery of the head of the human body (i.e., the
outside of the body cavity) in a state wherein the magnetic field
outside the body cavity has substantially the same strength as
one inside the head of the human body (i. e., the body cavity) .
The magnetic field distributed in the air is measured by the
triaxial MI sensors 5 (a to e), and the measurement signal is
processed in the exclusive signal processing circuit 6, thereby
obtaining the sensor output.
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Now, the sensor outputs finally required for detecting
the position and orientation of the tip of the insertion portion
2 of the catheter 1 is six, that is space coordinates (3 degrees
of freedom) and orientation angle (3 degrees of freedom) of the
permanent magnet 4. For example, in case of Fig. 4, from among
the triaxial MI sensors 5 (a to e) whose total number is five,
three triaxial MI sensors 5 (c to e) are not used, because they
have disadvantages wherein the permanent magnet 4 cannot approach
them owing to detecting environment and sensor installation
limiting condition or the like with the result that S/N ration
is small and measurement error is increased. As a result, only
the magnetic field measurement signals from two triaxial MI
sensors 5 (a, b) which are close to the permanent magnet 4 are
used, thereby making it possible to finally obtain six sensor
outputs whose S/N ratios are big enough though a tiny permanent
magnet 4, wherein the generatedmagnetic field strength is small,
is used.
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Outputs of two triaxial MI sensors 5 (a, b) thus obtained
are amplified in an amplification circuit 13. After that, they
are input to a computer PC through an A/D converter 14. Data
on a map made by previously gathering data about a position and
an angle is compared with actual detecting data from the triaxial
MI sensors 5 (a, b) by means of an well-known mapping method,
thereby making it possible to accurately detect the
three-dimensional position and orientation of the permanent
magnet 4, namely, the tip of the insertion portion 2 of the catheter
1. Moreover, on the basis of such detecting information, the
catheter 1 is indicated by superimposing it on a
three-dimensional blood vessel image G input to the computer
PC through CT and MRI previous to an operation. This can attain
a predetermined medical object of surely and easily inserting
the insertion portion 2 in the direction to be aimed, while
confirming safely and surely'the position and the orientation
of the tip of the insertion portion 2 of the catheter 1, without
unpleasantness caused by an operation performed in a state of
wearing a protector for avoiding a bad influence on the human
body and X-rays exposure owing to fluoroscopy.
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Though the above embodiment was described about a case
for applying the device to the catheter as the medical insertion
tool, it may be used as a guide wire and an endoscope except
the catheter. Moreover, it is applicable for detecting the
position and the direction of the tip of an indwelling tool in
vivio such as a drainage tube (ERBD tube) for forming a discharge
passage for body fluid, a biliary stent, a high calorie
transfusion tube, and a probe for thermotherapy in a vital tissue.
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Moreover, the permanent magnet 4 as the magnetic field
generating means may be disposed not only on the tip of the
insertion portion 2 of the catheter 1, but also on a number of
longitudinal positions thereof. Furthermore, by arranging a
low pass filter (LPF) for decreasing alternating current magnet
field noise occurred owing to peripheral devices, in the magnetic
field measurement signal processing circuit 6, a measurement
error is further decreased. This can enhance a detecting
accuracy.